Started following some tutorial on att85 usi. Downloaded example code from make avr book.

Make AVR Examples/Chapter17_I2C/loggingThermometer/loggingThermometer.c

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+
+
+// ------- Preamble -------- //
+#include <avr/io.h>
+#include <util/delay.h>
+#include <avr/interrupt.h>
+#include <avr/power.h>
+
+#include "pinDefines.h"
+#include "USART.h"
+
+#include "i2c.h"                                  /* for i2c functions */
+#include "25LC256.h"                            /* for EEPROM specific */
+
+// -------- Defines --------- //
+
+#define LM75_ADDRESS_W 0b10010000
+#define LM75_ADDRESS_R 0b10010001
+#define LM75_TEMP_REGISTER           0b00000000
+#define LM75_CONFIG_REGISTER         0b00000001
+#define LM75_THYST_REGISTER          0b00000010
+#define LM75_TOS_REGISTER            0b00000011
+
+#define CURRENT_LOCATION_POINTER  0
+          /* where to store a pointer to the current reading in EEPROM */
+#define SECONDS_POINTER           2
+                                     /* store seconds-delay value here */
+#define MEMORY_START              4
+                          /* where to start logging temperature values */
+#define MENU_DELAY                5
+                         /* seconds to wait before bypassing main menu */
+
+// -------- Functions --------- //
+
+static inline void printTemperature(uint8_t tempReading) {
+                                   /* temperature stored as 2x Celcius */
+  printByte((tempReading >> 1));
+  if (tempReading & 1) {
+    printString(".5\r\n");
+  }
+  else {
+    printString(".0\r\n");
+  }
+}
+
+int main(void) {
+  uint16_t secondsDelay;          /* how long to wait between readings */
+  uint16_t currentMemoryLocation;           /* where are we in EEPROM? */
+  uint16_t i;                        /* used to count memory locations */
+  uint8_t tempHighByte, tempLowByte, temperatureByte;     /* from LM75 */
+  uint8_t enterMenu;                                   /* logical flag */
+
+  // -------- Inits --------- //
+  clock_prescale_set(clock_div_1);                            /* 8 MHz */
+  initSPI();
+  initI2C();
+  initUSART();
+  LED_DDR |= (1 << LED0);
+
+                                    /* Load up last values from EEPROM */
+  secondsDelay = EEPROM_readWord(SECONDS_POINTER);
+
+                            /* Delay to allow input to enter main menu */
+  printString("*** Press [m] within ");
+  printByte(MENU_DELAY);
+  printString(" seconds to enter menu. ***\r\n ");
+
+  for (i = 0; i < MENU_DELAY; i++) {
+    _delay_ms(1000);
+  }
+
+  if (bit_is_set(UCSR0A, RXC0) && (UDR0 == 'm')) {
+    enterMenu = 1;
+  }
+  else {
+    enterMenu = 0;
+  }
+
+  while (enterMenu) {
+    printString("\r\n====[  Logging Thermometer ]====\r\n  ");
+    currentMemoryLocation = EEPROM_readWord(CURRENT_LOCATION_POINTER);
+    printWord(currentMemoryLocation - MEMORY_START);
+    printString(" readings in log.\r\n  ");
+    printWord(secondsDelay);
+    printString(" seconds between readings.\r\n");
+    printString(" [<] to shorten sample delay time\r\n");
+    printString(" [>] to increase sample delay time\r\n");
+    printString(" [?] to reset delay time to 60 sec\r\n");
+    printString(" [d] to print out log over serial\r\n");
+    printString(" [e] to erase memory\r\n");
+    printString(" [s] to start logging\r\n\r\n");
+
+    switch (receiveByte()) {
+    case 'd':
+      SLAVE_SELECT;
+      SPI_tradeByte(EEPROM_READ);
+      EEPROM_send16BitAddress(MEMORY_START);
+      for (i = MEMORY_START; i < currentMemoryLocation; i++) {
+        SPI_tradeByte(0);
+        printTemperature(SPDR);
+      }
+      SLAVE_DESELECT;
+      break;
+    case '<':
+      if (secondsDelay >= 10) {
+        secondsDelay -= 5;
+        EEPROM_writeWord(SECONDS_POINTER, secondsDelay);
+      }
+      break;
+    case '>':
+      if (secondsDelay < 65000) {
+        secondsDelay += 5;
+        EEPROM_writeWord(SECONDS_POINTER, secondsDelay);
+      }
+      break;
+    case '?':
+      secondsDelay = 60;
+      EEPROM_writeWord(SECONDS_POINTER, secondsDelay);
+      break;
+    case 'e':
+      printString("Clearing EEPROM, this could take a few seconds.\r\n");
+      EEPROM_clearAll();
+      EEPROM_writeWord(CURRENT_LOCATION_POINTER, MEMORY_START);
+      EEPROM_writeWord(SECONDS_POINTER, secondsDelay);
+      break;
+    case 's':
+      printString("OK, logging...\r\n");
+      enterMenu = 0;
+      break;
+    default:
+      printString("Sorry, didn't understand that.\r\n");
+    }
+  }
+
+  // ------ Event loop ------ //
+  while (1) {
+
+    currentMemoryLocation = EEPROM_readWord(CURRENT_LOCATION_POINTER);
+
+                                      /* Make sure in temperature mode */
+    i2cStart();
+    i2cSend(LM75_ADDRESS_W);
+    i2cSend(LM75_TEMP_REGISTER);
+                                          /* Get Temp from thermometer */
+    i2cStart();               /* Setup and send address, with read bit */
+    i2cSend(LM75_ADDRESS_R);
+    tempHighByte = i2cReadAck();           /* two bytes of temperature */
+    tempLowByte = i2cReadNoAck();
+    i2cStop();
+    temperatureByte = (tempHighByte << 1) | (tempLowByte >> 7);
+         /* temperatureByte now contains 2x the temperature in Celcius */
+    printTemperature(temperatureByte);                /* serial output */
+
+                                     /* Save the new temperature value */
+    EEPROM_writeByte(currentMemoryLocation, temperatureByte);
+
+    /* move on to next location and record new position
+       if not already at the end of memory */
+    if (currentMemoryLocation < EEPROM_BYTES_MAX) {
+      currentMemoryLocation++;
+      EEPROM_writeWord(CURRENT_LOCATION_POINTER, currentMemoryLocation);
+    }
+
+                                                              /* delay */
+    for (i = 0; i < secondsDelay; i++) {
+      _delay_ms(1000);
+      LED_PORT ^= (1 << LED0);             /* blink to show working */
+    }
+
+  }                                                  /* End event loop */
+  return 0;                            /* This line is never reached */
+}